Genetic Control of Mosquitoes: population suppression strategies

Over the last two decades, morbidity and mortality from malaria and dengue fever among other pathogens are an increasing Public Health problem. The increase in the geographic distribution of vectors is accompanied by the emergence of viruses and diseases in new areas. There are insufficient specific therapeutic drugs available and there are no reliable vaccines for malaria or dengue, although some progress has been achieved, there is still a long way between its development and actual field use. Most mosquito control measures have failed to achieve their goals, mostly because of the mosquito's great reproductive capacity and genomic flexibility. Chemical control is increasingly restricted due to potential human toxicity, mortality in no target organisms, insecticide resistance, and other environmental impacts. Other strategies for mosquito control are desperately needed. The Sterile Insect Technique (SIT) is a species-specific and environmentally benign method for insect population suppression, it is based on mass rearing, radiation mediated sterilization, and release of a large number of male insects. Releasing of Insects carrying a dominant lethal gene (RIDL) offers a solution to many of the drawbacks of traditional SIT that have limited its application in mosquitoes while maintaining its environmentally friendly and species-specific utility. The self-limiting nature of sterile mosquitoes tends to make the issues related to field use of these somewhat less challenging than for self-spreading systems characteristic of population replacement strategies. They also are closer to field use, so might be appropriate to consider first. The prospect of genetic control methods against mosquito vectored human diseases is rapidly becoming a reality, many decisions will need to be made on a national, regional and international level regarding the biosafety, social, cultural and ethical aspects of the use and deployment of these vector control methods.

Urotensin-II System in Genetic Control of Blood Pressure and Renal Function.

Urotensin-II controls ion/water homeostasis in fish and vascular tone in rodents. We hypothesised that common genetic variants in urotensin-II pathway genes are associated with human blood pressure or renal function. We performed family-based analysis of association between blood pressure, glomerular filtration and genes of the urotensin-II pathway (urotensin-II, urotensin-II related peptide, urotensin-II receptor) saturated with 28 tagging single nucleotide polymorphisms in 2024 individuals from 520 families; followed by an independent replication in 420 families and 7545 unrelated subjects. The expression studies of the urotensin-II pathway were carried out in 97 human kidneys. Phylogenetic evolutionary analysis was conducted in 17 vertebrate species. One single nucleotide polymorphism (rs531485 in urotensin-II gene) was associated with adjusted estimated glomerular filtration rate in the discovery cohort (p = 0.0005). It showed no association with estimated glomerular filtration rate in the combined replication resource of 8724 subjects from 6 populations. Expression of urotensin-II and its receptor showed strong linear correlation (r = 0.86, p<0.0001). There was no difference in renal expression of urotensin-II system between hypertensive and normotensive subjects. Evolutionary analysis revealed accumulation of mutations in urotensin-II since the divergence of primates and weaker conservation of urotensin-II receptor in primates than in lower vertebrates. Our data suggest that urotensin-II system genes are unlikely to play a major role in genetic control of human blood pressure or renal function. The signatures of evolutionary forces acting on urotensin-II system indicate that it may have evolved towards loss of function since the divergence of primates.

Genetic control of grain yield and nitrogen use efficiency in tropical maize

The objectives of this work were to study the genetic control of grain yield (GY) and nitrogen (N) use efficiency (NUE, grain yield/N applied) and its primary components, N uptake efficiency (NUpE, N uptake/N applied) and N utilization efficiency (NUtE, grain yield/N uptake), in maize grown in environments with high and low N availability. Experiments with 31 maize genotypes (28 hybrid crosses and three controls) were carried out in soils with high and low N rates, in the southeast of the state of Minas Gerais, Brazil. There was a reduction of 23.2% in average GY for maize grown in soil with low N, in comparison to that obtained with high N. There were 26.5, 199 and 400% increases in NUtE, NUpE, and NUE, respectively, for maize grown with low N. The general combining ability (GCA) and specific combining ability (SCA) were significant for GY, NUE and NUpE for maize grown in high N soil. Only GCA was significant for NUpE for maize grown in low N soil. The GCA and SCA for NUtE were not significant in either environment. Additive and non-additive genetic effects are responsible for the genetic control of NUE and GY for maize grown in soils with high N availability, although additive effects are more important.

Interference of genotypes x environments interaction in the genetic control of resistance to Asian rust soybean

The objectives of this work were to identify parents resistant to Asian soybean rust using diallel crosses, obtain information on the genetic control of soybean resistance to the pathogen and verify whether the combining ability estimates interact with the environment (year or time of assessment). The F1 generation was obtained in a greenhouse from crosses between five contrasting parents for the trait resistance to soybean rust, in a complete diallel without reciprocals. Two rust-severity assessments were carried out on individual soybean plants of 25 treatments (parents and F2 and F3 populations) in 2006/2007 and 2007/2008, in an experimental field at Embrapa Soja, Londrina, PR, Brazil. Additive effects predominated in the genetic control of soybean resistance to Asian rust, and the interaction of the segregant populations with the environment, although significant, did not alter the genetic parameter's general combining ability (GCA) and specific combining ability estimates, indicating that estimates obtained in one year and one assessment can be extrapolated to others. BR01-18437 inbred line is resistant to Asian rust and showed high GCA effects. This line should be used as parent if the objective is the resistance to Phakopsora pachyrhizi.

Genetic control of potassium content of common bean seeds

The objective of this work was to investigate possible maternal effects on potassium content of common bean seeds, as well as to estimate the heritability and selection gains in early hybrid generations for this character and to evaluate the efficiency of genetic selection to improve the nutritional quality of common bean (Phaseolus vulgaris). Crosses with four cultivars from the Mesoamerican gene pool yielded the reciprocal F1 and F2 generations and the backcrossed populations (BCP1 and BCP2). The potassium content of the progenies was measured via nitric‑perchloric digestion and flame photometry. The potassium content in the tested progenies varied from 6.0 to 14.9 g kg-1 dry matter, and no significant maternal effect was observed. The narrow-sense heritability ranged from low (33.26%) to intermediate (43.05%). Partial dominance was observed for low potassium content in the seeds. No increase in potassium content was obtained through selection. Breeding common bean plants for increasing potassium content in seeds may be difficult because the local environment strongly influences the character.

Genetic control of iron concentration in Mesoamerican and Andean common bean seeds

The objective of this work was to evaluate the main differences in the genetic control of the iron concentration in Mesoamerican and Andean common bean seeds, in early generations, and to select recombinants with a high iron concentration in the seeds. F1, F1 reciprocal, F2, F2 reciprocal, and backcross (BC11 and BC12) generations were produced by crosses between Mesoamerican (CNFP 10104 x CHC 01-175) and Andean (Cal 96 x Hooter) inbred lines. The expression of significant maternal effect was observed for the Mesoamerican gene pool. Iron concentration was higher in the seed coat of Mesoamerican common bean seeds (54.61 to 67.92%) and in the embryo of Andean common bean seeds (69.40 to 73.44%). High broad-sense heritability was obtained for iron concentration in Mesoamerican and Andean common bean seeds. Gains with the selection of higher magnitude, from 20.39 to 24.58%, are expected in Mesoamerican common bean seeds. Iron concentration in common bean seeds showed a continuous distribution in F2, which is characteristic of quantitative inheritance in Mesoamerican and Andean common bean seeds. Recombinants with high iron concentration in seeds can be selected in both Mesoamerican and Andean common bean hybrids.

Population Variation and Genetic Control of Modular Chromatin Architecture in Humans.

Chromatin state variation at gene regulatory elements is abundant across individuals, yet we understand little about the genetic basis of this variability. Here, we profiled several histone modifications, the transcription factor (TF) PU.1, RNA polymerase II, and gene expression in lymphoblastoid cell lines from 47 whole-genome sequenced individuals. We observed that distinct cis-regulatory elements exhibit coordinated chromatin variation across individuals in the form of variable chromatin modules (VCMs) at sub-Mb scale. VCMs were associated with thousands of genes and preferentially cluster within chromosomal contact domains. We mapped strong proximal and weak, yet more ubiquitous, distal-acting chromatin quantitative trait loci (cQTL) that frequently explain this variation. cQTLs were associated with molecular activity at clusters of cis-regulatory elements and mapped preferentially within TF-bound regions. We propose that local, sequence-independent chromatin variation emerges as a result of genetic perturbations in cooperative interactions between cis-regulatory elements that are located within the same genomic domain.

Genetic control of characters associated with bean golden mosaic geminivirus resistance in Phaseolus vulgaris L.

Bean golden mosaic is the most important viral disease of the bean crop (Phaseolus vulgaris L.) in Latin America. The genetics of resistance to a Brazilian strain of bean golden mosaic virus (BGMV), was studied in a 4 x 4 diallel cross without reciprocals, among the parental genotypes DOR 303, EMGOPA 201 Ouro, Carnaval, and Redlands Greenleaf C. Seedlings of the four parents, six F1 hybrids, 12 backcrosses, and F2 generations for each combination were inoculated on the eighth day after sowing by exposure to a viruliferous whitefly (Bemisia tabaci Genn.) population for 24 h, in a glasshouse, prior to transplantation to field conditions. The full set of two parents, F1, F2 and respective backcrosses for each combination was considered to be a family. Data were recorded and analyzed for foliar yellowing, plant dwarfing, and pod malformation, using a randomized block design, with two replications. Weighted generation mean analysis was performed for each of the six families. An additive gene action model was significant for the three characteristics evaluated. On the other hand, non-additive gene action had greater absolute value in most cases. Resistance to foliar yellowing conferred by genes from DRO 303 was highly heritable and was expressed equally well in the different genetic backgrounds evaluated. Such resistance may be oligogenic. Broad- and narrow-sense heritabilities were relatively high for all response traits. The three traits studied were all positively correlated, indicating that they can be simultaneously selected for enhancement. The highest correlation coefficient was obtained for dwarfing x pod malformation.

Genetic Control of Residual Variance for Teat Number in Pigs

The genetic improvement in litter size in pigs has been substantial during the last 10-15 years. The number of teats on the sow must increase as well to meet the needs of the piglets, because each piglet needs access to its own teat. We applied a genetic heterogeneity model on teat numberin sows, and estimated medium-high heritability for teat number (0.5), but low heritability for residual variance (0.05), indicating that selection for reduced variance might have very limited effect. A numerically positive correlation (0.8) between additive genetic breeding values for mean and for variance was found, but because of the low heritability for residual variance, the variance will increase very slowly with the mean.

Genetic control of fruit-setting percentage of tomatoes tolerant to high temperatures

The aim of present work was to study, through means and variances of generations, the genetic control of fruit-set percentage in tomatoes, in a biparental cross between line Jab-95 (resistant to fruit-set) and 'Caribe' cultivar (susceptible to fruit-set) after being subjected to high temperatures. F1, F2, and backcross generations for both parents (P 1, P2) were produced in a greenhouse at FCAVUNESP, Jaboticabal-SP, Brazil. A randomized complete block experimental design with four replications was used to evaluate the different generations. Estimates of genetic parameters were obtained according to Mather and Jinks (1982). An additive-dominant model was fitted to explain the variation observed. The mean degree of dominance (0.54), indicated incomplete dominance in the direction of increasing fruit-set percentage at high temperatures. The genetic control of fruit-set percentage, at high temperatures, for tomato was found to be oligogenic or polygenic (3.54 genes). The heritability in a limited sense was 83.91%, suggesting that the selection of individuals based on the characteristic evaluated can be efficient.

Genetic Control of Mosquitoes: population suppression strategies

Over the last two decades, morbidity and mortality from malaria and dengue fever among other pathogens are an increasing Public Health problem. The increase in the geographic distribution of vectors is accompanied by the emergence of viruses and diseases in new areas. There are insufficient specific therapeutic drugs available and there are no reliable vaccines for malaria or dengue, although some progress has been achieved, there is still a long way between its development and actual field use. Most mosquito control measures have failed to achieve their goals, mostly because of the mosquito's great reproductive capacity and genomic flexibility. Chemical control is increasingly restricted due to potential human toxicity, mortality in no target organisms, insecticide resistance, and other environmental impacts. Other strategies for mosquito control are desperately needed. The Sterile Insect Technique (SIT) is a species-specific and environmentally benign method for insect population suppression, it is based on mass rearing, radiation mediated sterilization, and release of a large number of male insects. Releasing of Insects carrying a dominant lethal gene (RIDL) offers a solution to many of the drawbacks of traditional SIT that have limited its application in mosquitoes while maintaining its environmentally friendly and species-specific utility. The self-limiting nature of sterile mosquitoes tends to make the issues related to field use of these somewhat less challenging than for self-spreading systems characteristic of population replacement strategies. They also are closer to field use, so might be appropriate to consider first. The prospect of genetic control methods against mosquito vectored human diseases is rapidly becoming a reality, many decisions will need to be made on a national, regional and international level regarding the biosafety, social, cultural and ethical aspects of the use and deployment of these vector control methods.

Characterization of the genetic control of fruit flesh color in peach

The analysis of a carotenoid cleavage dioxygenase gene in a pool of peach cultivars revealed the existence of a functional allele (W1), associated with the white flesh trait, and three independent mutations associated with the yellow phenotype: a 2 bp insertion within a repetitive sequence (y1), a large transposable element within the intron (y2) and a single base substitution generating a premature stop codon (y3). Based on these evidences, the yellow flesh phenotype seems to have arisen from at least three independent mutational events.

Genetic Control of Plant Development by Overriding a Geometric Division Rule

Formative cell divisions are critical for multicellular patterning. In the early plant embryo, such divisions follow from orienting the division plane. A major unanswered question is how division plane orientation is genetically controlled, and in particular whether this relates to cell geometry. We have generated a complete 4D map of early Arabidopsis embryogenesis and used computational analysis to demonstrate that several divisions follow a rule that uses the smallest wall area going through the center of the cell. In other cases, however, cell division clearly deviates from this rule, which invariably leads to asymmetric cell division. By analyzing mutant embryos and through targeted genetic perturbation, we show that response to the hormone auxin triggers a deviation from the ``shortest wall'' rule. Our work demonstrates that a simple default rule couples division orientation to cell geometry in the embryo and that genetic regulation can create patterns by overriding the default rule.